Purpose – The purpose of this paper is to systematically and critically review the literature related to process design and modeling of fused deposition modeling (FDM) and similar extrusion-based additive manufacturing (AM) or rapid prototyping processes. Design/methodology/approach – A systematic review of the literature focusing on process design and mathematical process modeling was carried out. Findings – FDM and similar processes are among the most widely used rapid prototyping processes with growing application in finished part manufacturing. Key elements of the typical processes, including the material feed mechanism, liquefier and print nozzle; the build surface and environment; and approaches to part finishing are described. Approaches to estimating the motor torque and power required to achieve a desired filament feed rate are presented. Models of required heat flux, shear on the melt and pressure drop in the liquefier are reviewed. On leaving the print nozzle, die swelling and bead cooling are considered. Approaches to modeling the spread of a deposited road of material and the bonding of polymer roads to one another are also reviewed. Originality/value – To date, no other systematic review of process design and modeling research related to melt extrusion AM has been published. Understanding and improving process models will be key to improving system process controls, as well as enabling the development of advanced engineering material feedstocks for FDM processes.

Purpose -The purpose of this paper is to critically review the literature related to dimensional accuracy and surface roughness for fused deposition modeling and similar extrusion-based additive manufacturing or rapid prototyping processes. Design/methodology/approach -A systematic review of the literature was carried out by focusing on the relationship between process and product design parameters and the dimensional and surface properties of finished parts. Methods for evaluating these performance parameters are also reviewed. Findings -Fused deposition modeling ® and related processes are the most widely used polymer rapid prototyping processes. For many applications, resolution, dimensional accuracy and surface roughness are among the most important properties in final parts. The influence of feedstock properties and system design on dimensional accuracy and resolution is reviewed. Thermal warping and shrinkage are often major sources of dimensional error in finished parts. This phenomenon is explored along with various approaches for evaluating dimensional accuracy. Product design parameters, in particular, slice height, strongly impact surface roughness. A geometric model for surface roughness is also reviewed. Originality/value -This represents the first review of extrusion AM processes focusing on dimensional accuracy and surface roughness. Understanding and improving relationships between materials, design parameters and the ultimate properties of finished parts will be key to improving extrusion AM processes and expanding their applications.

A population of meadow voles (Microtus pennsylvanicus) 75 mi northeast of Winnipeg, Manitoba, Canada was live—trapped biweekly for two winters. From August to February of each year the mean population weight decreased by 30% to 40%. This decrease was not due to preferential death of the heavier animals because their survival was better than would have been expected if survival and weight were independent. part of the weight loss was due to the immigration of young animals that failed to gain weight. However, much of the decrease in mean weight was due to that lost by individuals, because many samples of animals released and recaptured 2 wk later had lost significant amounts of weight. Four marked ♂ ♂ trapped from August to February lost an average of 28.6% of their weights while 14 marked ♀ ♀ lost 45.5% in the same time period. In February the mean weights of individuals and the population began to increase. It is suggested that weight loss is not simply a result of lack of food, but is an adaptive response cued by some factor such as day length.

Intraspecific aggression of male Microtus pennsylvanicus drummondii was observed in 320 10-minute paired encounters in a neutral arena, during 17 months. Voles were drawn from a population live-trapped biweekly at Pinawa, Manitoba. The 17 months were divided into the following reproductive periods: non-breeding, testes scrotal, and littering. There were two non-breeding, two testes scrotal periods, and a single littering period. Threats, vocalizing, and "mutual uprights" were significantly and positively associated in all but one of the periods. Together with fighting, these three acts formed the aggressive component of the behavior recorded. All aggressive acts increased in frequency as males became reproductively active, and decreased as the breeding season ended. Latencies to aggressive acts were negatively related to the acts' frequencies. Less frequent acts (fighting, "grooming other," and "submissives") also showed seasonal changes associated with breeding: fighting was common throughout the breeding period, submissives most common early in the reproductive period, and grooming other most prevalent when juveniles were present in the population. Incidences of tail-wounding in the field population were significantly more common during the breeding season, and in males. A comprehensive Index of Aggression was devised by means of principal component analysis, based on the total frequencies of aggressive acts. Mean Indices of Aggression for the five periods showed that aggressive levels in the three breeding periods were significantly higher than in the two non-breeding periods. Re-tests of 53 voks showed score-·. ll·lm their two encounters to be positively correlated.Aggression mea'.u! .l 'n the encounters was related to population parameters derived from live-trapping results. Breeding season home ranges were larger than winter home ranges. Overwintered adults were more aggressive, had larger home ranges and survived longer than young of the year. Aggression and survival were positively related in adults but not in young. Resident voles were more aggressive than non-residents. Dominant voles were usually slightly heavier. Pairs of voles of similar weight exhibited more aggressive acts, but "following" was more frequent in dissimilar weight pairs. Aggressive levels did not vary consistently with population density.These observations demonstrate there is an annual cycle of intraspecific aggression synchronized with the breeding season in male M. pennsylvanicus. They support studies on Peromyscus, which also showed that aggression increased with spring breeding and declined as reproduction ceased in fall; thus, behavioral density regulation seems most likely to occur during the breeding period.

The population cycles of meadow voles (Microtus pennsylvanicus) were studied in southeastern Manitoba, Canada, from 1968 to 1978 on a 32—ha old field and in surrounding boreal forest. Vole density was monitored on mark—recapture live—trapping at 2— to 4—wk intervals throughout the year. This was supplemented by a 3—d spring and a 30—d summer snap—trapping survey. Multiannual and annual fluctuations in density of Microtus were independent of a diversity of patterns seen in other small mammal species. Principal components analysis of demographic statistics was used to characterize changes in seasonal reproduction, survival, and dispersal that accounted for the observed numerical fluctuations. Conditions during a catastrophic winter population decline in 1970—1971 were compared with those in 1974—1975, when numbers recovered quickly after a modest spring decline. Voles were in good condition before and during both declines, as evidenced by normal body composition indices. Large body masses, characteristic of peak populations, preceded both population declines. The main conditions associated with the 1970—1971 decline were unusual patterns in social behavior and dispersal. Changes in social behavior in the field were reflected in unprecedented numbers of multiple captures in Longworth traps before and during this decline. Field observations were supported by unusually high frequencies of amicable behavior in neutral arena bouts staged between males removed from a control population. Little dispersal was detected with conventional live—trapping during the winter period of chronic mortality in 1971. In contrast, a period of acute mortality, resulting in the near extinction of the population in March 1971, was associated with considerable dispersal. We propose two alternative hypotheses consistent with the unpredictable and episodic nature of vole population declines: (1) an immunological dysfunction exists in voles that makes them susceptible to naturally occurring microparasites or (2) opportunistic, pathogenic microparasites exploit the changes in dispersal and social contacts that occur as a normal part of the vole population cycle.